Steel making process



Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE:

lic Steel Corporation, Youngstown, Ohio, a corporation of New Jersey NoDrawing. ApplicationApril 18,1935, Serial No. 17,138

4 Claims.

This invention relates tothe manufacture of steel, and particularly to amethod of controlling the abrasiveness of non-metallic substances insteel.

Highly abrasive non-metallic substances are usually present in steelsproduced by present day methods. When a steel containing such substancesis machined, these substances quickly dull and wear the cutting tools sothat the life of such tools is short.

I have found that the degree of ab asiveness of such substances can begreatly redu ed with coincident prolongation of cutting tool life. Thereduction I have accomplished has increased the cutting tool life by100% or more without any attendant disadvantages.

The present invention is predicated on the discovery that theabrasiveness of non-metallic substances normally formed by chemicalreactions in the molten steel during its manufacture, is traceablelargely to the amount and form of manganese and associated non-metallicmanganese compounds present in the steel; and on the discovery thatalteration of the form of such manganese and manganese compounds willresult in a change in the degree of abrasiveness of the non-metallicsubstances in the steel.

Briefly described, the present invention includes the steps of makingmolten steel in any suitable manner, determining the approximatecomposition of the steel and substances there'- in, and the nature andamounts of non-metallic forming ingredients, particularly manganese and.associated metallic compounds in the steel, and treating the steel in amanner to give the desired properties to the non-metallic substances inthe steel.

The present invention will be better understood by those skilled in theart by the following examples in which it may be practiced.

Steel to be machined was made by the usual Bessemer practice. Itcontained the usual amounts of impurities including sulphur, phosphorus,as well as non-metallic substances such as silicates, the approximateamounts of which were known, and about .05% of manganese in metallic andnon-metallic form. About 1.25% of manganese, in the form offerromanganese, was added in solid form to the steel during pouring andwhen the ladle was about one-quarter filled with steel. after themanganese had been added, about 4 pounds of siderite (FeCOz) per ton ofsteel was thrown into the ladle, the pouring being continued until theladle was filled. The siderite During pouring, and preferably justevidently decomposed, liberating oxygen or an oxygen containing gas. Themetal in the ladle was violently agitated and gas was evolved, and

, the resulting steel was relatively free from abrasive, non-metallicsubstances as measured by 5 cutting tool life which was more than doublethe life obtained on similar steel made in the same way except for theaddition of the siderite.

The content of. manganese in metallic and nonmetallic forms, in-thesteel of the foregoing example before the addition of the ferromanganesewas, as stated, about .05%, and after treatment with the siderite wasabout .90%. If no siderite or equivalent material had been added themanganese content would have been about 1.00%. Thus the present processtends to remove some of the manganese which would otherwise remain inthe steel. This tendency is important, for if it be disregardeddifiiculty in finishing a steel within the limits of manganese specifiedmay be encountered, particularly in open hearth steels high inmanganese.

The amount of siderite or its equivalent which should be used in mymethod will vary somewhat with the manganese desired inthe finishedsteel. For example, the variation per ton of steel is on about the orderof 4 pounds of siderite for .80% of manganese, '7 pounds for 1.00% ofmanganese and 10 pounds for 1.50% of manganese.

It is important to determine the amount of 3 manganese in the steel inmetallic and nonmetallic forms as a preliminary to determination of theamount of siderite or its equivalent to use. If toosmall an amount ofsiderite is used, 35 the degree of abrasiveness of the non-metallicsubstances will not be greatly decreased, while if too large an amountis used the manganese content in the finished steel may be lower than isdesired. Also the cost may be unduly increased be-' 40 cause of undueloss of manganese and waste of siderite or its equivalent. I believethat there is a fairly well defined balance between the amounts ofmanganese present in metal form, and in nonmetallic substances in steeland that when this balance is disturbed there is a tendency forreestablishment of the balance. Consequently, it is important to knownthe manganese content before determining how much siderite or itsequivalents to use. Knowledge of the amounts of ingredients used to makea given steel and the manner in which the given steel was made areusually sufiicient for this purpose and the making of a chemicalanalysis is not necessary.

Substances, other than siderite, which possess the property of reducingthe abrasiveness oi the non-metallic substances in steel include ironoxide ores such as limonite, phosphate ores such as viviam'te, and slowacting non-ferrous carbonates such as cerussite, rhodochrosite malachiteand azurite. In general, any substance which will liberate oxygen or anoxygen containing gas in the molten steel rapidly, but not so rapidly asto result in an explosion, may be used. Combinations of two or more ofthese substances may be used. Although ores are mentioned because oftheir relatively low cost, substances which contain the oxygen compoundsof these ores may be used satisfactorily. Sodium carbonate decomposestoo rapidly for safe use, for it tends to explode and throw molten metalout of the ladle.

Ibelieve that the treatment of steel with substances which decomposerapidly, but not too rapidly, in the steel, and liberate oxygen or anoxygen containing gas, bring about an oxidation of manganese and ironwith resultant fluxing of the MnO with ,FeO and lowering of the fusingtemperature; and that substances such as iron silicates, manganesesilicates, iron manganese silicates, MnO, corresponding aluminates andother substances which are ordinarily relatively iniusible, andtherefore highly abrasive, are converted by such oxidizing or fluxingactions into more readily fusible substances, even into substances whichmelt at temperatures below the melting point of steel, with coincidentdecrease in abrasiveness. Moreover, I believe that the decrease inmelting points of such substances with the agitation due to evolution ofgas in the steel results in movement of considerable quantities ofsuchsubstances into the slag, thus reducing the amount of such substancesremaining in the steel when cold.

This invention is applicable to open hearth steels such as killed andrimming steels, steels having above about .80% of Mn, and steels inwhich the Mn is high to counteract high sulphur. This method may becarried out on open hearth steel with good results as follows: Tap themolten'steel into a ladle, adding the predetermined amount offerromanganese when the ladle is about one-fourth filled and then addthe calculated amount of siderite or other equivalent substances beforeslag covers the metal in the ladle. Alternatively, some of the manganesemay be added in the furnace, if desired.

The invention is also of advantage with electric furnace steels. Themetal is tapped while hot andthe siderite or other equivalent is addedin predetermined amount to the ladle during flow of the steel into theladle.

Having thus described my invention so that those skilled in the art mayunderstand and be able to practice the same, what I desire to secure byLetters Patent is defined in what is claimed.

What is claimed is:

1. The process of making steel which includes the steps of makingBessemer steel containing about .05% of manganese, adding about 1.25% ofmanganese to such steel while it is being poured into a ladle, andadding between about four and seven pounds of siderite per ton of steelto the steel during pouring into the ladle.

2. The process of making steel which includes the steps of making steelcontaining between about .80% and about 1.5% of manganese andnon-metallic substances, and mixing with such steel, while molten,between about four pounds and about ten pounds of siderite per ton ofsteel.

3. The process of making steel which includes the steps of making, bythe open hearth process, steel containing manganese and othernonmetallic substance-forming ingredients, adding manganese to suchmolten steel to bring the total manganese content of the steel tobetween about .80% and about 1.50%, and treating the molten about .80%and about 1.50% of manganese and 40' from the group consisting ofsiderite and llmonite H per ton of steel.

EARL C. SMITH.

